Example HTTP Response
HTTP/1.1 510 Not Extended- Required HTTP extension not present
- Missing mandatory extension header
- Extended functionality required
What does this mean?
Need more info! The server requires additional extensions or features that weren't included in your request.
Technical Definition
Further extensions to the request are required for the server to fulfill it.
RFC Says
"The 510 (Not Extended) status code indicates that further extensions to the request are required for the server to fulfill it. The server may include information about what extensions are required in the response."
Plain English:
510 means 'Your request needs additional HTTP extensions that you didn't include.' This is from RFC 2774 (HTTP Extension Framework), which never gained widespread adoption. It's essentially a theoretical status code for negotiating HTTP extensions.
Common Misinterpretation
You should never need to use 510 in modern applications. The HTTP Extension Framework it was designed for is obsolete. If your API needs additional information, use 400 Bad Request with a clear error message instead.
Ready-to-use code for returning this HTTP status in your application:
// Express.js
app.get('/example', (req, res) => {
res.status(510).json({
error: 'Not Extended',
message: 'Your error message here'
});
});
// Native HTTP
const http = require('http');
http.createServer((req, res) => {
res.writeHead(510, { 'Content-Type': 'application/json' });
res.end(JSON.stringify({
error: 'Not Extended',
message: 'Your error message here'
}));
}).listen(3000);